Flame-retardant cellulose-based solid polymer electrolyte as well as preparation method and application thereof

Abstract

The invention relates to a flame-retardant cellulose-based solid polymer electrolyte as well as a preparation method and application thereof, and belongs to the technical field of new energy materials and electrochemistry. The preparation method of the flame-retardant cellulose-based solid polymer electrolyte comprises the following steps: taking cellulose as a raw material, and reacting with a phosphorus-containing compound to prepare a phosphorus-modified cellulose polymer with intrinsic flame retardance; dissolving the phosphorus-modified cellulose polymer in a solvent, and mixing with a lithium salt and a polymer matrix to form uniform slurry; and casting, drying and curing the slurry to obtain the solid polymer electrolyte membrane. The solid polymer electrolyte membrane has excellent flame retardant property, high ionic conductivity and good mechanical strength and interface stability. The raw materials are wide in source, green and environment-friendly, the preparation process is simple, large-scale production is easy, and the prepared solid polymer electrolyte membrane can remarkably improve the safety of a lithium battery and has a wide application prospect.

Description

Technical Field

[0001] This invention belongs to the field of new energy materials and electrochemical technology, specifically relating to a flame-retardant cellulose-based solid polymer electrolyte, its preparation method, and its application. Background Technology

[0002] With the widespread application of electric vehicles, portable electronic devices, and energy storage systems, their safety has become an increasingly important concern. Traditional liquid lithium-ion batteries use liquid electrolytes, which pose safety hazards such as easy leakage, flammability, and explosion, severely hindering their further development. Solid-state electrolytes, as the core component of next-generation lithium-ion batteries, are considered the ultimate solution to the safety issues of lithium batteries and are expected to be matched with high-capacity lithium metal anodes, thereby achieving higher energy densities.

[0003] Currently, solid-state electrolytes mainly fall into two categories: inorganic ceramic / glass electrolytes and organic polymer electrolytes. Inorganic electrolytes (such as LLZO and LATP) possess high ionic conductivity and excellent mechanical strength, but they are typically brittle and hard, resulting in poor solid-solid interface contact with the electrode, high interfacial impedance, and complex and costly manufacturing processes. Polymer solid-state electrolytes offer advantages such as good flexibility, ease of processing, and excellent compatibility with the electrode interface, making them promising candidates for flexible lithium-ion batteries. However, their room-temperature ionic conductivity is generally low, and most polymer matrices (such as PEO and PVDF) are inherently flammable, failing to meet practical application requirements.

[0004] To impart flame retardancy to polymer solid electrolytes, flame retardants, such as phosphate ester liquid additives or inorganic hydroxides, are often added to the electrolyte. However, traditional flame retardants are mostly small molecule compounds, which are prone to migration and aggregation in the polymer matrix. This not only reduces the mechanical properties of the solid electrolyte but also affects the ion transport efficiency, leading to a decrease in ionic conductivity.

[0005] Cellulose, as a natural polymer material, boasts advantages such as wide availability, environmental friendliness, low cost, and excellent mechanical properties. Introducing it into polymer solid electrolytes can enhance the electrolyte's mechanical properties and structural stability. However, pure cellulose lacks flame-retardant properties and ion transport capabilities. Phosphorus is a highly efficient flame-retardant element; introducing phosphorus into the cellulose molecular chain through chemical bonding can prepare phosphorus-modified cellulose with intrinsic flame retardancy. Using it as a matrix and loading lithium salt ion conductors holds promise for constructing a composite solid electrolyte that combines high safety, high ionic conductivity, and good mechanical properties.

[0006] Therefore, developing a method that can effectively improve the flame retardant properties and ionic conductivity of polymer solid electrolytes, while having a simple preparation process and low cost, has become an urgent technical problem to be solved in the field of solid electrolytes. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a flame-retardant cellulose-based solid polymer electrolyte, its preparation method, and its applications. This invention modifies cellulose to impart flame-retardant properties, and simultaneously utilizes the synergistic effect of modified cellulose and the polymer matrix to improve the microstructure and ion transport channels of the electrolyte, thereby achieving a synergistic improvement in the flame retardancy and high ionic conductivity of the solid electrolyte.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows:

[0009] A method for preparing a flame-retardant cellulose-based solid polymer electrolyte includes the following steps:

[0010] (1) Preparation of modified cellulose:

[0011] Cellulose raw materials and phosphorus-containing compounds are reacted at 60-120℃ for 2-24 hours. After the reaction is completed, the mixture is washed and dried to obtain phosphorus-modified cellulose polymer.

[0012] (2) Preparation of the mixture:

[0013] The phosphorus-modified cellulose polymer, polymer matrix and lithium salt obtained in step (1) are placed in an organic solvent and stirred thoroughly to disperse them evenly, so as to obtain a uniform and stable composite electrolyte slurry, which is the mixture.

[0014] (3) Preparation of composite solid electrolytes:

[0015] The mixture obtained in step (2) is poured into a mold, and after drying and demolding, a flame-retardant cellulose-based solid polymer electrolyte is obtained.

[0016] Preferably, in step (1), the cellulose is one or more of microcrystalline cellulose (MCC), nanocellulose (NC), cellulose nanofibers (CNF), cellulose nanocrystals (CNC), powdered cellulose (PC), carboxymethyl cellulose (CMC), bacterial cellulose (BC), methyl cellulose (MC), wood pulp, and cellulose acetate (CA).

[0017] Preferably, in step (1), the phosphorus-containing compound is selected from one or more of dimethyl vinylphosphonate (DMVP), divinylphenylphosphonate (DVBPA), 2-carboxyethylphenylphosphonic acid (CEPPA), m-phenylenediamine phenylphosphonic acid (MPDPA), phosphorus trichloride (PCl3), phosphorus oxychloride (POCl3), hexachlorocyclotriphosphazene (HCCP), phytic acid (IP6), dimethyl phosphite (DMHP), phenylphosphonodichlorophenoxychloride (BPOD), diphenylphosphonodichlorophenoxychloride (DPPCl), 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), or derivatives thereof, and its phosphorus content accounts for 2%-10% of the mass of the phosphorus-modified cellulose polymer.

[0018] Preferably, in step (2), the polymer matrix is ​​polyethylene oxide (PEO) or polyvinylidene fluoride (PVDF), and the mass of the polymer matrix accounts for 5-90% of the mass of the phosphorus-modified cellulose polymer.

[0019] Preferably, in step (2), the lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide (LiNTf2), lithium bis(fluorosulfonyl)imide (LiFSI), lithium trifluoromethanesulfonate (LiCF3SO3), lithium hexafluorophosphate (LiPF6), and lithium perchlorate (LiClO4), and the mass of the lithium salt accounts for 5-50% of the mass of the phosphorus-modified cellulose polymer.

[0020] Preferably, in step (2), the organic solvent is one or a mixture of several of N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), acetonitrile (ACN), or an ionic liquid.

[0021] A flame-retardant cellulose-based solid polymer electrolyte prepared by the above preparation method.

[0022] Preferably, the composite solid electrolyte has an ionic conductivity ≥1×10⁻⁶ at 25°C. -3 S cm -1 Tensile strength ≥25MPa, limiting oxygen index ≥28%, flame retardancy rating reaches UL94 V-0.

[0023] Application of a flame-retardant cellulose-based solid polymer electrolyte in lithium-ion batteries.

[0024] Furthermore, the flame-retardant cellulose-based solid polymer electrolyte is used in flexible lithium-ion batteries.

[0025] The beneficial effects of this invention are:

[0026] The preparation method of the flame-retardant cellulose-based solid polymer electrolyte of the present invention has the following advantages:

[0027] (1) Intrinsic high safety: By introducing phosphorus flame retardant elements into the cellulose skeleton through chemical bonding, the electrolyte matrix is ​​endowed with intrinsic and permanent flame retardancy, eliminating the need to add easily migratable and volatile liquid flame retardants, thus fundamentally eliminating the risk of combustion.

[0028] (2) Environmentally friendly and low cost: It uses cellulose as a raw material, which is widely available, renewable and biodegradable, in line with the concept of green and sustainable development, and is inexpensive.

[0029] (3) Excellent overall performance: Modified cellulose has good mechanical properties and can improve the tensile strength of solid electrolytes to over 25 MPa as a reinforcing phase. At the same time, the three-dimensional network structure further enhances the structural stability of the electrolyte, preventing deformation or breakage during charging and discharging.

[0030] (4) Simple process and easy to scale up: The preparation process of this invention is simple, requires no complicated equipment, has a wide range of raw material sources and low cost, is easy to scale up production, and has good industrial application prospects.

[0031] (5) The flame-retardant cellulose-based solid polymer electrolyte prepared can be widely used in the field of lithium-ion batteries, especially suitable for flexible lithium-ion batteries with high safety requirements. Attached Figure Description

[0032] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0033] Figure 1 The image shows the infrared spectrum of the phosphorus-modified cellulose polymer prepared in Example 1 of this invention.

[0034] Figure 2 This is a scanning electron microscope image of the phosphorus-modified cellulose polymer prepared in Example 1 of the present invention.

[0035] Figure 3 The ionic conductivity test curve (25°C) of the composite solid electrolyte membrane prepared in Example 1 of the present invention.

[0036] Figure 4 To test the Li / Li symmetric battery assembled using the composite solid electrolyte prepared in Example 1 of this invention at 1 mA / cm² -2 Cyclic performance at current density. Detailed Implementation

[0037] The preparation method of a flame-retardant cellulose-based solid polymer electrolyte of the present invention will be described more clearly and in more detail below, including the following steps:

[0038] (1) Preparation of modified cellulose

[0039] The dried cellulose raw material is dispersed in an appropriate amount of solvent (such as acetonitrile, N,N-dimethylformamide, etc., in an amount 20-50 times the mass of the cellulose raw material) and stirred to form a suspension. A phosphorus-containing compound and NaOH are added, and the mixture is reacted at 60-120℃ for 2-24 hours under an inert atmosphere and nitrogen protection. After the reaction is complete, the mixture is cooled to room temperature. The precipitate is collected by filtration or centrifugation and repeatedly washed with ethanol to remove unreacted raw materials and catalyst. Finally, it is dried to constant weight in a vacuum oven at 60-80℃ to obtain a black or pale yellow phosphorus-modified cellulose polymer.

[0040] The cellulose is preferably one or more of microcrystalline cellulose (MCC), nanocellulose (NC), cellulose nanofibers (CNF), cellulose nanocrystals (CNC), powdered cellulose (PC), carboxymethyl cellulose (CMC), bacterial cellulose (BC), methyl cellulose (MC), wood pulp, and cellulose acetate (CA).

[0041] The phosphorus-containing compound is preferably selected from one or more of dimethyl vinylphosphonate (DMVP), divinylphenylphosphonate (DVBPA), 2-carboxyethylphenylphosphonic acid (CEPPA), m-phenylenediamine phenylphosphonic acid (MPDPA), phosphorus trichloride (PCl3), phosphorus oxychloride (POCl3), hexachlorocyclotriphosphazene (HCCP), phytic acid (IP6), dimethyl phosphite (DMHP), phenylphosphonodichlorophenoxychloride (BPOD), diphenylphosphonodichlorophenoxychloride (DPPCl), 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), or their derivatives, and its phosphorus content accounts for 2%-10% of the mass of the phosphorus-modified cellulose polymer.

[0042] (2) Preparation of the mixture

[0043] The phosphorus-modified cellulose polymer obtained in step (1) is added to an organic solvent (such as NMP or DMSO) and stirred to prepare a homogeneous polymer solution with a concentration of 5-50 wt%. While continuously stirring, a calculated amount of lithium salt is added to the polymer solution, and stirring continues until the lithium salt is completely dissolved. Then, a certain amount of polymer matrix is ​​added, and high-speed mechanical stirring is used to uniformly disperse the polymer matrix in the polymer solution, forming a homogeneous, stable, and viscous composite electrolyte slurry, which is the mixture.

[0044] In this process, phosphorus-modified cellulose polymers serve as flame-retardant fillers and reinforcing phases, enhancing the flame retardancy and mechanical properties of the electrolyte while improving its structural stability. The polymer matrix provides a carrier for ion transport, lithium salts act as the ion source, and organic solvents are used to dissolve the components, forming a uniform dispersion system.

[0045] The polymer matrix is ​​preferably polyethylene oxide (PEO) or polyvinylidene fluoride (PVDF), and the mass of the polymer matrix accounts for 5-90% of the mass of the phosphorus-modified cellulose polymer.

[0046] The lithium salt is preferably one or more of lithium bis(trifluoromethanesulfonyl)imide (LiNTf2), lithium bis(fluorosulfonyl)imide (LiFSI), lithium trifluoromethanesulfonate (LiCF3SO3), lithium hexafluorophosphate (LiPF6), and lithium perchlorate (LiClO4), and the mass of the lithium salt accounts for 5-50% of the mass of the phosphorus-modified cellulose polymer.

[0047] The organic solvent is preferably one or a mixture of several of N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), acetonitrile (ACN), or ionic liquids.

[0048] (3) Preparation of composite solid electrolytes

[0049] The mixture obtained in step (2) is poured into a clean mold. The mold is then transferred to a vacuum drying oven to remove the organic solvent and form a solid film. Finally, the film is demolded to obtain a flame-retardant cellulose-based solid polymer electrolyte.

[0050] This invention also provides a flame-retardant cellulose-based solid polymer electrolyte prepared by the above method. The thickness of this solid electrolyte is controllable (typically 80-200 μm), its flame retardancy rating reaches UL94 V-0 (tested according to UL94-2013 standard), and its ionic conductivity at 25°C is ≥1.0 × 10⁻⁶. -3 S cm -1 (Tested according to GB / T12967.4-2014 standard), tensile strength ≥25MPa (tested according to GB / T 1040.3-2006 standard), exhibiting good flame retardancy, ionic conductivity, and mechanical properties. Simultaneously, this composite solid electrolyte demonstrates good interfacial compatibility with lithium-ion battery electrodes and excellent cycle stability, retaining ≥99% capacity after 100 cycles at 1C rate. Furthermore, due to the introduction of phosphorus, this electrolyte exhibits excellent flame retardant properties, with a limiting oxygen index (LOI) of not less than 28% (tested according to GB / T 2406.2-2009 standard).

[0051] The flame-retardant cellulose-based solid polymer electrolyte prepared by this invention can be widely used in the field of lithium-ion batteries, and is especially suitable for flexible lithium-ion batteries with high safety requirements.

[0052] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0053] The following are examples of preparing composite solid electrolytes using a single cellulose raw material and a single phosphorus-containing compound.

[0054] Example 1

[0055] 1. Preparation of modified cellulose:

[0056] 2.0 g of microcrystalline cellulose (MCC) was weighed and dispersed in 20 mL of N,N-dimethylformamide (DMF), and sonicated for 40 min. 0.5 g of hexachlorocyclotriphosphazene (HCCP) and 0.1 g of NaOH were added as catalysts. The reaction was carried out at 90 °C for 12 h under nitrogen protection. After the reaction was complete, the mixture was cooled to room temperature, the precipitate was collected by filtration, and washed three times with an ethanol-water solution. The product was dried in a vacuum oven at 60 °C for 24 h to obtain a black powder of hexachlorocyclotriphosphazene-modified cellulose polymer (MCC / P-1).

[0057] 2. Preparation of the mixture:

[0058] By mass, 1 g of MCC / P-1 was dissolved in 1 g of N-methylpyrrolidone and magnetically stirred for 6 hours until completely dissolved, yielding a 50 wt% mixed solution. 0.5 g of lithium bis(trifluoromethanesulfonyl)imide (LiNTf2) was added to this solution and stirred until completely dissolved. Then, 0.9 g of PEO powder (the polymer matrix constituted 90% of the mass of the phosphorus-modified cellulose polymer) was added. The mixture was transferred to a planetary ball mill jar and ball-milled at 300 rpm for 8 hours to ensure uniform dispersion of the components, yielding a homogeneous slurry, which is the mixed solution.

[0059] 3. Preparation of composite solid electrolytes:

[0060] The mixture was poured into a polytetrafluoroethylene (PTFE) mold, which was then transferred to a vacuum drying oven at 60°C for 8 hours. After demolding, a flame-retardant composite solid electrolyte based on hexachlorocyclotriphosphide modified cellulose polymer with a thickness of 150 μm was obtained, namely, a flame-retardant cellulose-based solid polymer electrolyte. The resulting electrolyte membrane was designated MCC / P-M1.

[0061] 4. Performance Testing:

[0062] The test results are as follows: The composite solid electrolyte prepared in this embodiment has a flame retardancy rating of UL94 V-0 (tested according to UL94-2013 standard), and an ionic conductivity of 1.2 × 10⁻⁶ at 25℃. -3 S cm -1(Tested according to GB / T12967.4-2014 standard), the tensile strength is 25 MPa (tested according to GB / T 1040.3-2006 standard), and the limiting oxygen index is 30% (tested according to GB / T 2406.2-2009 standard). It is assembled into a CR2032 type lithium-ion battery, and at 1 mA cm⁻¹... -2 After 900 cycles at the specified rate, the capacity retention rate is ≥99%.

[0063] Example 2-11

[0064] Examples of the modified cellulose preparation system provided by the present invention in phosphorus-containing compounds with functionalized groups. The steps of Examples 2-11 are the same as those of Example 1, and the specific conditions and results are shown in Table 1, and the properties are shown in Table 2.

[0065] Table 1. Modified cellulose prepared by reacting a single cellulose feedstock with a single phosphorus-containing compound.

[0066]

[0067]

[0068] Table 2 Performance parameters of modified cellulose prepared by reacting a single cellulose feedstock with a single phosphorus-containing compound.

[0069]

[0070] The following are examples of preparing composite solid electrolytes using mixed cellulose raw materials or mixed phosphorus-containing compounds.

[0071] Example 12

[0072] 1. Preparation of modified cellulose:

[0073] Weigh 1.0 g of microcrystalline cellulose (MCC) and 1.0 g of powdered cellulose (PC), mix them, disperse them in 50 mL of DMF, and sonicate for 30 min. Add 0.5 g of phenylphosphonic dichloride (BPOD) and 0.1 g of NaOH as catalysts, and react at 90 °C for 12 h under nitrogen protection. Filter, wash, and vacuum dry at 60 °C for 24 h to obtain phenylphosphonic dichloride modified cellulose polymer (MCC / PC / P-12).

[0074] 2. Preparation of the mixture:

[0075] Dissolve 1g of MCC / PC / P-12 in 1g of N-methylpyrrolidone and stir for 6 hours to obtain a 50wt% solution. Add 0.5g of LiNTf2, stir to dissolve, and then add 0.9g of PEO (the polymer matrix accounts for 90% of the mass of the phosphorus-modified cellulose polymer). Ball mill for 8 hours to obtain a slurry, which is the mixture.

[0076] 3. Preparation of composite solid electrolytes:

[0077] After casting the mixture obtained in step 2, vacuum dry it at 60°C for 8 hours and demold to obtain a composite solid electrolyte membrane with a thickness of 150 μm, namely the flame-retardant cellulose-based solid polymer electrolyte, denoted as MCC / PC / P-M12.

[0078] 4. Performance Testing:

[0079] The test results are as follows: The composite solid electrolyte prepared in this embodiment has a flame retardant rating of UL94 V-0 and an ionic conductivity of 1.2 × 10⁻⁶ at 25°C. -3 S cm -1 Tensile strength 26 MPa, limiting oxygen index 30%; capacity retention 97.5% after 2000 battery cycles.

[0080] Examples 13-20

[0081] Examples of the modified cellulose preparation system provided by this invention in phosphorus-containing compounds with functionalized groups. The steps in Examples 13-20 are the same as in Example 12; the specific conditions and results are shown in Table 3, and the properties are shown in Table 4.

[0082] Table 3. Modified cellulose prepared by reacting mixed cellulose raw materials with mixed phosphorus-containing compounds.

[0083]

[0084]

[0085] Table 4 Performance parameters of modified cellulose prepared by reacting mixed cellulose raw materials with mixed phosphorus-containing compounds

[0086]

[0087] Comparative Example 1

[0088] This comparative example prepared an unmodified cellulose-based electrolyte. The phosphorus modification treatment in step 1 was omitted; microcrystalline cellulose (MCC) was used directly, and the remaining steps were the same as in Example 1. The specific steps are as follows:

[0089] Preparation of the mixture: Unmodified cellulose-based electrolyte was prepared in this comparative example. The phosphorus modification reaction in step 1 was omitted, and microcrystalline cellulose (MCC) was used directly. In step 2, 1 g of MCC was dispersed in 1 g of NMP, followed by the addition of LiTFSI and 1 g of PEO, and the mixture was ball-milled for an extended period (12 h) to attempt to homogenize it. After casting and drying, the resulting film was brittle and had an uneven surface. This film is denoted as MCC-D1.

[0090] Performance testing and characterization:

[0091] 1. Structural characterization: Figure 1 Fourier transform infrared (FT-IR) spectroscopy was performed on the MCC / P-1 obtained in Example 1. The FT-IR was measured at 904 cm⁻¹. -1 A distinct characteristic absorption peak of the ester carbonyl group (C=O) appeared nearby, and at 1240 cm⁻¹ -1 The significantly enhanced intensity of the P=N characteristic peak within the range proves that hexachlorocyclotriphosphazene has been successfully grafted onto the cellulose molecular chain.

[0092] 2. Morphological characteristics: Figure 2 The scanning electron microscope (SEM) images of MCC / P-1 obtained in Example 1 were tested. A three-dimensional network structure was observed in the SEM, demonstrating that hexachlorocyclotriphosphazene was successfully grafted onto the cellulose molecular chain.

[0093] 3. Verification of Ionic Conductivity: The electrolyte membranes prepared in Examples 1-20 and Comparative Example 1 were cut into circular pieces with a diameter of 1.6 cm and assembled into stainless steel|electrolyte|stainless steel (SS|SS) symmetric cells. The impedance was measured by electrochemical impedance spectroscopy (EIS) at 25 °C, and the ionic conductivity was calculated (σ=d / (R×A), where d is the film thickness, R is the bulk resistance, and A is the electrode area). Figure 3 The ionic conductivity test curve of the composite solid electrolyte membrane prepared in Example 1 at 25°C shows that its conductivity reaches 1.2 × 10⁻⁶. -3 S cm -1 In Comparative Example 1, MCC-D1 exhibited very low ionic conductivity (<1.1 × 10⁻⁶) due to undissolved cellulose and extremely poor interfacial contact. -4 S cm -1 ).

[0094] 4. Lithium dendrite suppression capability test: MCC / P-M1 was assembled into a Li|MCC-1|Li symmetric cell, and the lithium dendrite suppression capability was tested at 1 mA cm⁻¹. -2 A constant current cycling test was performed at a current density of 0.5 h, with commutation every 0.5 h. Figure 4 The battery maintained a stable and low polarization voltage (80mV) for more than 450 hours without short circuit, indicating that the electrolyte has good interfacial stability and excellent lithium dendrite suppression capability.

[0095] 4. Flame retardant performance test: The flame retardant rating is tested according to the UL94 vertical burning standard. The sample size is 127mm×12.7mm×0.1-0.3mm (matching the actual thickness of the solid electrolyte membrane). The burning rate, dripping phenomenon and self-extinguishing time are recorded to determine the rating. The limiting oxygen index (LOI) is tested according to the GB / T 2406.1-2008 standard. The sample size is 80mm×10mm×0.1-0.3mm. The minimum oxygen concentration required to sustain combustion is determined in an oxygen-nitrogen mixed gas flow.

[0096] 5. Tensile strength and elongation at break were tested using a universal testing machine (model: Instron 5967). The samples were machined into a dumbbell shape (conforming to GB / T 1040.3-2006 standard), and the tensile rate was set to 5 mm / min. -1 Each sample was tested 5 times, and the average value was taken.

[0097] In summary, the preparation method of the phosphorus-modified cellulose polymer-based flame-retardant composite solid electrolyte of the present invention involves using cellulose as a raw material and reacting it with a phosphorus-containing compound to prepare phosphorus-modified cellulose with intrinsic flame retardancy; dissolving the phosphorus-modified cellulose in a solvent, and then mixing it with lithium salt and a polymer matrix to form a homogeneous slurry; the slurry is then cast, dried, and cured to obtain a composite solid electrolyte membrane. This membrane possesses excellent flame retardant properties, high ionic conductivity, good mechanical strength, and interfacial stability. The raw materials of the present invention are widely available and environmentally friendly, the preparation process is simple and easy to scale up, and the prepared solid electrolyte can significantly improve the safety of lithium batteries, showing broad application prospects.

[0098] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for producing a flame-retardant cellulose-based solid-state polymer electrolyte, characterized by, The preparation method comprises the following steps: (1) preparation of modified cellulose: reacting cellulose raw material with phosphorus-containing compound at 60-120℃ for 2-24h, and then washing and drying to obtain phosphorus-modified cellulose polymer; (2) preparation of mixed solution: placing phosphorus-modified cellulose polymer prepared in step (1), polymer matrix and lithium salt in organic solvent, fully stirring to uniformly disperse, to obtain uniform and stable composite electrolyte slurry, which is mixed solution; (3) preparation of composite solid electrolyte: casting the mixed solution prepared in step (2) into a mold, and then drying and demolding to obtain flame-retardant cellulose-based solid polymer electrolyte.

2. The production method according to claim 1, characterized by, In step (1), the cellulose is one or more of microcrystalline cellulose (MCC), nanocellulose (NC), cellulose nanofibril (CNF), cellulose nanocrystal (CNC), powder cellulose (PC), carboxymethyl cellulose (CMC), bacterial cellulose (BC), methyl cellulose (MC), wood pulp and cellulose acetate (CA).

3. The preparation method according to claim 1, characterized in that, In step (1), the phosphorus-containing compound is one or more of dimethyl vinylphosphonate (DMVP), divinylbenzene phosphonate (DVBPA), 2-carboxyethyl phenyl phosphinic acid (CEPPA), m-phenylenediamine phenyl phosphonic acid (MPDPA), phosphorus trichloride (PCl3), phosphorus oxychloride (POCl3), hexachlorocyclotriphosphazene (HCCP), phytic acid (IP6), dimethyl phosphite (DMHP), benzophosphoryl dichloride (BPOD), diphenyl phosphinic dichloride (DPPCl), 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) or derivatives thereof, and the phosphorus content is 2%-10% of the mass of the phosphorus-modified cellulose polymer.

4. The method of claim 1, wherein, In step (2), the polymer matrix is polyethylene oxide (PEO) or polyvinylidene fluoride (PVDF), and the mass of the polymer matrix is 5-90% of the mass of the phosphorus-modified cellulose polymer.

5. The preparation method according to claim 1, characterized in that, In step (2), the lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide (LiNTf2), lithium bis(fluorosulfonyl)imide (LiFSI), lithium trifluoromethylsulfonate (LiCF3SO3), lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), and the mass of the lithium salt is 5-50% of the mass of the phosphorus-modified cellulose polymer.

6. The method of claim 1, wherein, In step (2), the organic solvent is a mixed solvent of one or more of N-methyl pyrrolidone (NMP), dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), acetonitrile (ACN) or ionic liquid.

7. A flame-retardant cellulose-based solid polymer electrolyte prepared by the preparation method of any one of claims 1-6.

8. The flame-retardant cellulose-based solid-state polymer electrolyte according to claim 7, characterized by, Its ionic conductivity at 25°C is ≥ 1 x 10 -3 S cm -1 , tensile strength ≥ 25 MPa, limiting oxygen index ≥ 28%, and the flame retardant level reaches UL94 V-0 level.

9. Application of the flame-retardant cellulose-based solid polymer electrolyte of claim 7 in a lithium ion battery.

10. Use according to claim 9, characterized in that, 9. Application of the flame-retardant cellulose-based solid polymer electrolyte of claim 7 in a lithium ion battery.

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